Objective: To determine whether an association exists between the histopathologic diagnosis of adenomyosis and infertility in a population of captive baboons. Design: Case-control study. Setting: Southwest National Primate Research Center. Animal(s): Necropsy records of 37 baboons diagnosed with adenomyosis uteri and 38 baboons with normal uterine histology. Intervention(s): None. Main Outcome Measure(s): chi(2) analysis of the association between adenomyosis, primary infertility, and the presence of coexisting endometriosis. Result(s): Endometriosis was associated with the presence of adenomyosis (OR = 31.5, 95% CI 4.2-1,348). There was a trend toward an association of endometriosis with the presence of lifelong infertility, but this correlation did not quite achieve statistical significance (OR = 3.6, 95% CI 0.9-15.8). Adenomyosis was associated with the presence of lifelong infertility (OR = 20.6, 95% CI 2.7-897). This association was maintained when cases of coexisting endometriosis (n = 17) were excluded (OR = 20.1, 95% CI 2.1-921). Conclusion(s): Adenomyosis is strongly associated with lifelong primary infertility in the baboon, even in the absence of coexisting endometriosis. (C) 2004 by American Society for Reproductive Medicine.